Wetting pigment dispersion

A variety of additives are used to control the properties of wetting and dispersion of pigments, flow, Hthography, and mb-off of inks. These additives belong to classes of materials such as surfactants, bentonite clays, alkyds, functional resins, polymers, etc. 

Water-Based Writing Inks. These consist of very fine pigment dispersions in aqueous media containing small amounts of glycol or glycerol and a dispersing aid. They dry mainly by evaporation and quick wetting of ceUulosic fibers in paper substrates. 

Average temperatures (40-70°C) in combination with high-shear dispersion equipment, of which three-roll mills are a good example, appear to afford the best results in terms of pigment dispersion in wetting systems, such as offset varnish. Fig. 33 shows a curve in which the degree of dispersion reaches a distinct maximum at one particular temperature. 

In organic systems wetting and dispersion of the pigments is usually quite easy but stabilization of the dispersions normally requires steric stabilization, provided by adsorbed layers of polymer molecules. It appears that in most cases the adsorbed polymer layer has to be greater than about 10 nm for such dispersions to be sufficiently stable [782]. 

For colored products, pigments may be added during blending. These can be added dry directly to the powder prior to the addition of the lubricant, or as a wet blend in the lubricant. In the latter case, the pigment dispersion is added with the remaining lubricant. 

The adhesion of various coatings can depend on the properties of surfactants. Pigment wetting and dispersancy in the formulation of a product is initially of importance but the wetting out of the coated surface is also often dependent on the properties of surfactants. Even highway marking tapes that indicate temporary lanes during construction phases are areas where surfactants play a critical role in the effectiveness of the products. 

Is an excellent solvent for dyes and pigments with improved oxidative stability. It can be directly substituted for castor oil to wet pigment more rapidly for faster dispersions. 

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